1. Field of the Invention
The present invention relates generally to an apparatus for and method of carrying a substrate and, more particularly, to a substrate carrying apparatus and method for use with a semiconductor manufacturing system or a system for manufacturing a substrate for a liquid crystal.
2. Related Background Art
FIG. 7 illustrates this type of conventional apparatus. A carry by the apparatus shown in FIG. 7 is conducted as follows. A substrate storage part 1 is for storing a plurality of substrate casings 2 for encasing substrates R. The substrate R is stored in each casing. The substrate R is taken out of the substrate casing 2 by means of a carrier arm 3 and delivered to a carrier 4. The carrier 4 incorporates a prealignment mechanism. The substrate R is aligned to assume a predetermined state with respect to a carry target position. The prealignment mechanism consists of, e.g., four openable/closable pawl members. The substrate R is caught by the four pawl members, thereby effecting the prealignment. A fiducial position of the substrate R is determined by impinging surfaces of the four pawl members at that time.
The aligned substrate R is delivered to a load arm 5. Thereafter, the load arm 5 carries the substrate R to a reticle table 7. The substrate R that has completely undergone an exposure is delivered by an unload arm 6 to a carrier 4 from the reticle stage 7. Then, the substrate R is returned to a substrate storage part 1 in procedures reversed to the above-mentioned. With the operations described above, the substrate R is carried between the substrate storage part 1 and the reticle table 7. This type of apparatus is disclosed fully in Japanese Patent Application Laid-Open No. 62-195143.
Another practice is that some of a plurality of arms serve as temporary standby locations.
In the prior art discussed above, other sorts of substrates R required in one lot are stored in the substrate storage part 1 while being encased in the substrate casings 2. A position of the substrate R is not fixedly held (fixed) in the substrate casing 2. Exposing involves a step of effecting a prealignment each time (herein, a step through the carrier 4). Consequently, there arises such a problem that a carry route elongates correspondingly, and it is therefore impossible to reduce a substrate replacement cycle time.
Further, in the method where some of the carrier arms serve as the temporary standby locations, if there are large numbers of substrates to be repeatedly replaced, the substrates are returned to the aforementioned substrate storage part 1. Another substrate is required to be taken out of the substrate storage part 1 and carried to the temporary standby location. For this reason, a problem is caused, wherein a great number of substrates repeatedly replaceable in a short substrate replacement cycle can not be obtained.
Moreover, when the same number of carrier arms as that of the substrates R to be replaced are disposed in side by side relationship, the arms need a large space, and the whole apparatus becomes complicated. A moving distance of the carrier arm increases when loading and unloading the substrate R. This results in a decline in throughput of carrying the substrates. Under such circumstances, there exists a problem in which the number of the carrier arms can not be increased.